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Updated: Oct 23, 2026

Development and Application of Rapamycin-regulated Tyrosine Phosphatases
06:56

Development and Application of Rapamycin-regulated Tyrosine Phosphatases

Published on: September 6, 2024

Protein phosphatase 2A interacts with the 70-kDa S6 kinase and is activated by inhibition of

R T Peterson1, B N Desai, J S Hardwick

  • 1Howard Hughes Medical Institute, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.

Proceedings of the National Academy of Sciences of the United States of America
|April 14, 1999
PubMed

Insights

FKBP12-rapamycin-associated protein (FRAP) indirectly controls cell cycle regulators 4E-BP1 and p70(s6k) phosphorylation by restraining a phosphatase. Rapamycin or amino acid deprivation inhibits FRAP, leading to phosphatase activation and dephosphorylation of these key proteins.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • FKBP12-rapamycin-associated protein (FRAP), also known as mTOR, is a key regulator of translation initiation and cell cycle progression.
  • Previous studies suggested FRAP acts as a kinase, directly phosphorylating 4E-BP1 and p70(s6k) in response to stimuli.
  • Rapamycin treatment or amino acid deprivation inhibits FRAP, causing dephosphorylation and inactivation of 4E-BP1 and p70(s6k).

Purpose of the Study:

  • To investigate the mechanism by which FRAP regulates 4E-BP1 and p70(s6k) phosphorylation.
  • To determine if FRAP acts directly as a kinase or indirectly by modulating phosphatase activity.
  • To elucidate the role of phosphatases in the rapamycin and amino acid deprivation signaling pathways.

Main Methods:

  • Cell treatment with rapamycin and amino acid deprivation.
  • Analysis of protein phosphorylation using Western blotting.
  • In vitro kinase assays to assess FRAP activity towards PP2A.
  • Co-immunoprecipitation to study protein-protein interactions.

Main Results:

  • Evidence suggests FRAP indirectly controls 4E-BP1 and p70(s6k) phosphorylation by restraining a phosphatase.
  • A calyculin A-sensitive phosphatase is essential for p70(s6k) dephosphorylation induced by rapamycin or amino acid deprivation.
  • Rapamycin treatment increases protein phosphatase 2A (PP2A) activity towards 4E-BP1.
  • PP2A associates with p70(s6k), and FRAP phosphorylates PP2A in vitro.

Conclusions:

  • FRAP restrains PP2A activity, thereby preventing the dephosphorylation of 4E-BP1 and p70(s6k).
  • Amino acid deprivation or rapamycin treatment inhibits FRAP's ability to restrain PP2A, leading to the dephosphorylation of these targets.
  • This study proposes an indirect mechanism for FRAP's regulation of translation and cell cycle entry via phosphatase modulation.

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